Formation and Structure of Dialkyl Sulfide Self-Assembled Monolayers on Au(111)

Abstract

Surface structures, electrochemical properties, and binding conditions of self-assembled monolayers (SAMs) formed by dialkyl sulfides (DAS) with symmetric or unsymmetric dialkyl chains on Au(111) were investigated by means of scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV) measurements. STM imaging showed that the surface structures of DAS SAMs were markedly different from those of alkanethiol (AT) SAMs or dialkyl disulfide (DADS) SAMs. AT and DADS SAMs have hexagonal packed c(4 × 2) or a (√3 × √3)R30º structures containing many vacancy islands (VIs), whereas DAS SAMs have row structure with large ordered domains having a few VIs. These remarkable structural differences for DAS SAMs are due to intact adsorption of DAS molecules contrary to the dissociative adsorption of -S-H or -S-S- for AT or DADS on gold surfaces. We have also demonstrated that the formation and structure of DAS SAMs on Au(111) were markedly influenced by immersion time and solution temperature.